The hydrogen column density to Sirius B has yet to be
measured directly even though it is the nearest and
brightest white dwarf. The fundamental parameters of
temperature, radius, and mass of this important white dwarf
have remained uncertain, largely due to the difficulty of
observing a much fainter white dwarf in close proximity to
the brightest star in the sky, Sirius A. Recent spectral
measurements of Sirius B in the extreme ultraviolet (EUV),
which are free from contamination from Sirius A, have
allowed accurate determinations of the temperature and
gravity and therefore the radius of the white dwarf (Holberg
et al. 1998). However, these results depend critically on
the assumed H and He column density towards the source.
Holberg et al. rederived the H column using the UV
absorption lines of SiII, OI and CII measured with IUE and
scaled the results to hydrogen by adopting solar abundances
and characteristic depletion factors. Other estimates of the
H column have used the measured deuterium column scaled by
the D/H ratio determined towards other nearby stars (Bertin
et al, 1995), or by using other proxy elements such as MgII
(Frisch, 1994).

We will present an attempt to derive this neutral H column
directly, by measuring the Lyman continuum flux from Sirius
B above 50.4 nm using the long wavelength photometer
(Scanner C) on the Extreme Ultraviolet Explorer satellite
(EUVE). Neutral H is the only element in the ISM that can
significantly absorb this continuum at these low column
densities. During a five orbit observation on November 30,
1998, Sirius B was detected at a level of 0.022 counts per
second in the 60 nm (Tin) bandpass of EUVE. The H column
densities derived depend on the source models assumed. We
will discuss these dependencies as well as possible
systematic experimental errors.